Abstract
Abstract. This review is a synthesis of work spanning the last 25 yr. It is largely based on the use of climate networks to identify climate subsystems/major modes and to subsequently study how their collective behavior explains decadal variability. The central point is that a network of coupled nonlinear subsystems may at times begin to synchronize. If during synchronization the coupling between the subsystems increases, the synchronous state may, at some coupling strength threshold, be destroyed shifting climate to a new regime. This climate shift manifests itself as a change in global temperature trend. This mechanism, which is consistent with the theory of synchronized chaos, appears to be a very robust mechanism of the climate system. It is found in the instrumental records, in forced and unforced climate simulations, as well as in proxy records spanning several centuries.
Highlights
IntroductionSoon reports of fractality and low dimensionality in climate records and other geophysical data begun to surface
A study has shown how El Nino/Southern Oscillation (ENSO) with its effects on Pacific North America (PNA) can, through vertical propagation of the Rossby waves influence the lower stratosphere and how in turn the stratosphere can influence North Atlantic Oscillation (NAO) through downward progression of Rossby wave (Ineson and Scaife, 2009). These results coupled with our results suggest the following 3-D super-loop: NAO → Pacific Decadal Oscillation (PDO) → ENSO → PNA → stratosphere → NAO, which captures the essence of decadal variability in the Northern Hemisphere and possibly the globe
The findings presented here and in the references may settle the issue of dimensionality of climate variability over decadal scales, as they support the view that over these scales, climate collapses into distinct subsystems whose interplay dictates decadal variability
Summary
Soon reports of fractality and low dimensionality in climate records and other geophysical data begun to surface These climate records represented dynamics over different time scales ranging from very long (thousands of years; Nicolis and Nicolis, 1984) to very short (hours; Tsonis and Elsner, 1988). Every report suggested underlying attractors of dimensions between 3 and 8 These early results suggested that climate variability may be described by relatively few differential equations. In Tsonis and Elsner (1989), it was suggested that if low dimensional attractors exist they are associated with subsystems each operating at different space and/or time scales. In his study on dimension estimates, Lorenz (1991) concurs with the suggestion of Tsonis and Elsner (1989) These subsystems may be nonlinear and exhibit a variety of complex behaviors. If subsystems exist in the climate system what are they and what physics can we infer from them?
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